<template>
    <ul class="list">
        <li
                class="item"
                v-for="item of letters"
                :key="item"
                :ref="item"
                @touchstart="handleTouchStart"
                @touchmove="handleTouchMove"
                @touchend="handleTouchEnd"
                @click="handleLetterClick"
        >
            {{item}}
        </li>
    </ul>
</template>

<script>
    export default {
        name: "CityAlphabet",
        props: {
            cities: Object
        },
        computed: {
            letters () {
                const  letters = []
                for (let i in this.cities) {
                    letters.push(i)
                }
                return letters
            }
        },
        data () {
            return {
                touchStatus: false,
                startY: 0,
                timer: null
            }
        },
        updated () {
            this.startY = this.$refs['A'][0].offsetTop
        },
        methods: {
            handleLetterClick (e) {
                this.$emit('change',e.target.innerText)
            },
            handleTouchStart (e) {
                this.touchStatus = true
            },
            handleTouchMove (e) {
                if (this.touchStatus) {
                    if (this.timer) {
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(() => {
                        const touchY = e.touches[0].clientY - 79
                        const index = Math.floor((touchY - this.startY) / 20)
                        if (index >= 0 && index < this.letters.length) {
                            this.$emit('change',this.letters[index])
                        }
                    },16)
                }
            },
            handleTouchEnd () {
                this.touchStatus = false
            }
        }
    }
</script>

<style lang="stylus" scoped>
    @import "~styles/varibles.styl"
    .list
        display flex
        flex-direction column
        justify-content center
        position absolute
        top 1.58rem
        right 0
        bottom 0
        width .4rem
        .item
            line-height .4rem
            text-align center
            color $bgColor
</style>
